94 EX blowing PCM Fuses-need my work truck back..HELP | Ford Explorer Forums - Serious Explorations

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94 EX blowing PCM Fuses-need my work truck back..HELP

JOHN BUFF

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Joined
February 18, 2004
Messages
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City, State
WARWICK, R.I.
Year, Model & Trim Level
1994 EDDIE BAUER 4X4
Hello and thanks in advance.
yesterday my truck just died while doing about 35mph, I coasted to my jobsite and tried to restart it, all it did was turn over, I ended up disconnecting the fuel line at the intake, cranked it over, bone dry. checked the switch at passenger feet under carpet (it's o.k). Had AAA tow it home, and today started to trace fuel pump power supply from the pump. no power anywhere. Took apart the power distribution box, all relays were good. I have a blown 30A fuse that powers (or is labled) Power control module. I believe this also feeds the FP relay. I jumped a 12V wire to the FP relay, and heard the FP fire up, as well I got a supply of gas from the line. I am lost without my truck for work, as I am in the construction bus. I consider myself fairly knowledgable with vehicles, as I been fixing my own cars and trucks for 20+ years. Anybody had this problem before? Like to try ant quick fixes, before having to purchase a new PCM. I have a feeling the PCM shorted out. This problem happened all of the sudden, and the truck has been running great for years
1994 Eddy Bauer
4.0 auto A/C power everything
No mods
 



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no the EEC power and fuel pump power are not the same.
The PCM tells the fuel pump relay when to come on, so if the PCM is not on neither will the fuel pump.

Did you try replacing the fuse? I am going to assume you did and it blew again, correct?

First I would start off by opening up the power dist box, its not hard the rear cover snaps off, look for any wiring issues inside there.
If there is a question about the EEC or fuel pump relays, replace them, better now then later and they are a common issue on these early trucks.

It may be the EEC relay?

If all checks out is there anybody you know that has the same truck?
94, with the same transmission? You can swap the PCM and see if the problem goes away, otherwise start calling used part warehouses in search of a new PCM.
Dont freak out, I have seen about 6 of the Gen I trucks (pre 95) have a PCM fail, it can be a very difficult problem to diagnose and when they go, they go for good.....
Ford will sell you a remanu unit for like $200, dont get it. They are dogs, not as aggressive a profile as your 93 has, find one with the same calibration code used.

I can find them all day long in CO for about $30-60
 






thanks for the reply. I checked all the relays by placing them in one of the working slots of the distribution box, and each clicked. I did take the distibution box apart to look for any loose or corroded wires (no problems), and I did some probing. I jumped a 12v wire to the fp relay to make sure my fp was working, which it is. I blew a total of 3 fuses, and stopped there. I replace a fuse (30A for the pcm) turn key to on, and the fuse pops after 3 seconds. 1 more thing I noticed with the hood up. When I replaced the fuse and turned the key to the on position, there was a sound from the engine compartment, one that I have always heard, but it seemed to last longer. It's hard to discribe, but it sounds like my dodge truck used to sound when I turned the key on, there was a solenoid on the carb that used to set the idle, and it would make a metalic rattle of sorts...I know your saying what the hell is he talking about.
Thanks for any input
 












Hello, thanks for the reply.
I'm getting confused... I'm being directed towards a EEC problem but the power distribution box lables the fuse as Power Control Module. Is the PCM and the EEC one in the same, or does my truck have both? Also with the key on, if I pull the PCM relay and plug it bach in..it clicks, doesn't this mean that it is working properly, and not stuck in an open or closed position... EEC or PCM harnes looks fine also (talking about the silver box on the pass side kick panel.
Thanks to all who take the time to help others.
 






JOHN BUFF said:
Hello, thanks for the reply.
I'm getting confused... I'm being directed towards a EEC problem but the power distribution box lables the fuse as Power Control Module. Is the PCM and the EEC one in the same, or does my truck have both? Also with the key on, if I pull the PCM relay and plug it bach in..it clicks, doesn't this mean that it is working properly, and not stuck in an open or closed position... EEC or PCM harnes looks fine also (talking about the silver box on the pass side kick panel.
Thanks to all who take the time to help others.

1) The PCM and EEC are the same thing, those are just synonyms for the same part.

2) Just because the relay clicks doesn't mean its working. There still could be a short causing the fuse to blow.

3) Remove the relay, insert a new fuse, and turn the truck on. Does the fuse still blow? If yes, the the problem is most likley not the EEC or the relay, but something before the relay. If it does not blow, try a new relay. I'm not sure if its a generic relay, or a specific one. Autozone or Napa will know.
 






EEC=Electronic Engine Controls
PCM=Powertrain Control Module
I'm sure we could argue semantics over whether they refer to the same thing. Here's my take on it. PCM refers to the computer itself, which is mounted behind the passenger kick panel on your '94, I believe. The PCM is the central "brain" of the EEC system, which consists of the PCM and all the associated sensors and solenoids and such that go into the engine management.
The PCM fuse feeds power to the PCM. Unless there's a separate fuse labeled EEC, the PCM fuse also feeds power to the fuel pump relay, the HO2S heater, the MAF, and other solenoids/sensors that require a 12V power supply. Any of these components could be causing the PCM fuse to blow, as well as a short in any of the wiring. I would suggest a wiring diagram, if you don't already have one, and start working through it.
 






Thanks again to all the input.
Just went outside and pulled the EEC relay out, turned the key on, and the fuse DID NOT blow. I then put the relay back in, and the fuse blew. Now I switched around some of the other relays the other day to see if it was my FP relay that was bad, so I'm not sure if that last relay I pulled out was originally the EEC relay. I did though only switch around the relays that had the same ratings printed on them. Also I have a wiring diagram, but it's the one in the Haynes manual, which you all know is not as good as it could be.
Much thanks to the all knowing on this website, I've done alot of machanic work over the years, but electrical is a PITA
 






I am not familiar with first gens, but maybe someone with a wiring diagram can answer what's driven by that relay? Is it just the computer and sensors? Or are the O2 heaters on there as well?

They are most suseptible to damage when compared to other sensors and systems, IMO.
 






The wiring diagrams in the vehicle repair guides at www.autozone.com (same as in Chiltons) should be adequate for seeing what gets power through that fuse. O2 sensor heater doesn't get power through the EEC fuse/relay; I was wrong earlier.
 






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